1. Field of the Invention
The present invention pertains to microwave discharge lamps. More particularly, the present invention relates to such lamps with light reflective material inside the microwave cavity. The present invention also relates to sealed microwave lamp systems.
2. Related Art
Microwave discharge lamps are well known in the art. In operation, a magnetron or other source of microwave energy transmits microwave energy through a waveguide to a microwave cavity. An electrodeless bulb containing a fill is disposed in the microwave cavity. The microwave energy is coupled to the fill, which emits light when excited.
U.S. Pat. No. 5,334,913 issued to Ury et al. and entitled xe2x80x9cMicrowave Powered Lamp having a Non-conductive Reflector within the Microwave Cavityxe2x80x9d discloses a microwave discharge lamp which includes a reflector inside the microwave cavity. The internal reflector is typically used as a continuation of an external reflector to direct the light output.
FIG. 1 is a schematic view of a standard Light Drive(copyright) 1000 microwave discharge lamp commercially available from Fusion Lighting, Inc., Rockville, Md. USA. An enclosure 1 houses the magnetron and waveguide together with a power supply and control circuitry. Microwave energy is coupled to a microwave cavity 3 which is defined by a screen 4 having a solid portion 5 and a mesh portion 7. A bulb 9 is disposed in the microwave cavity 3. An external reflector 11 is mounted to the enclosure 1 around the microwave cavity 3. The bulb fill is typically a sulfur or selenium fill, for example, as described in U.S. Pat. No. 5,404,076.
As described in detail in U.S. Pat. No. 5,841,233, a dichroic mirror is mounted inside the microwave cavity 3. As shown in FIG. 2, the dichroic mirror 13 is mounted at a juncture between the solid portion 5 and the mesh portion 7 of the screen 4. The mirror 13 is used together with the external reflector 11 to direct the light output from the bulb 9. The bulb 9 is typically positioned at a focal point of the external reflector 11.
FIG. 3 is schematic, cross-sectional view of a microwave lamp with a reflective coating disposed on an interior surface of the microwave cavity, as disclosed in U.S. Pat. No. 5,903,091. A reflective coating 15 is disposed on the interior surface of a metal enclosure 17 which is configured as a resonant microwave cavity. A bulb 19 with no coating is also disposed within the enclosure 17. The enclosure defines an aperture 21 which is covered by a screen or mesh 23. Microwave energy is provided to the microwave cavity through a coupling slot. The energy is coupled to a fill in the bulb 19 which emits light when excited. The light exits the enclosure 17 primarily through the aperture 21.
It is an object of the invention to provide a microwave discharge lamp which utilizes light reflective material inside the microwave cavity. Specifically, it is an object of the invention to provide a high power aperture lamp which can be effectively coupled to external optical elements. It is another object of the invention to provide a sealed microwave discharge lamp system.
According to one aspect of the invention, an electrodeless microwave discharge lamp includes a source of microwave energy, a microwave cavity, a coupling structure configured to transmit the microwave energy from the source to the microwave cavity, a bulb disposed within the microwave cavity, the bulb including a discharge forming fill which emits light when excited by the microwave energy, and a reflector disposed within the microwave cavity and spaced from the bulb, wherein the reflector defines a reflective cavity which encompasses the bulb within its volume and a light emitting aperture, and wherein the reflective cavity has an inside surface area which is significantly less than an inside surface area of the microwave cavity. In most examples, at least a portion of the reflector is spaced from a wall of the microwave cavity.
In some examples, a portion of the reflector defining the light emitting aperture extends from a position closely spaced to an exterior surface of the bulb to a light transmissive end portion of the microwave cavity. For example, an inner diameter of the reflector is slightly larger than an outer diameter of the bulb. The reflector may comprise a hollow cylinder of reflective material which is open on both ends and the bulb is adapted to reflect light into the hollow cylinder. Alternatively, the reflector comprises a hollow cylinder of reflective material which is open on one end and substantially closed on the other end, wherein the open end defines the light emitting aperture. If the bulb is attached to a stem, the substantially closed end comprises an opening adapted to receive the stem. The closed end may be spaced away from the bulb or may be closely spaced to the bulb. In some examples, the bulb is spherically shaped and the closed end is hemispherically shaped and closely spaced to the bulb. The closed end may be relatively thicker than the walls of the cylinder to promote heat transfer from the bulb.
Preferably, the reflector is made from a non-conductive and highly reflective material. For example, the material comprises silica or alumina or a combination thereof.
In some examples, the microwave cavity is defined by a hollow metal cylinder with solid walls which is open on one end and closed on the other end except for an aperture, and wherein an outer diameter of the reflector is adapted to closely match a diameter of the microwave cavity aperture. In other examples, the microwave cavity is defined by a hollow metal cylinder with solid walls which is open on both ends, and wherein the reflector comprises a hollow cylinder of reflective material which is open on one end and substantially closed on the other end, wherein the open end of the reflective cylinder defines the light emitting aperture and wherein an outer diameter of the reflective cylinder is closely matched to an inner diameter of the metal cylinder. Advantageously, the metal cylinder defining the microwave cavity is structurally rigid and resistant to deformation. The closed end of the reflector may comprise a separate reflective disk. In most examples, the closed end of the reflective cylinder is spaced from a wall of the microwave cavity and may be closely spaced to the bulb.
Preferably, the microwave cavity is substantially sealed from environmental contamination. For example, if the microwave cavity is defined by a hollow metal cylinder with solid walls which includes an opening on one end in the area of the light emitting aperture, the opening may be covered by a quartz plate. In some examples, the quartz plate comprises a conductive mesh disposed thereon or embedded therein.
According to another aspect of the invention, an electrodeless lamp includes a resonant cavity, a bulb disposed in the resonant cavity, the bulb containing a discharge forming fill, a source of energy coupled to the fill, and a dielectric material in the resonant cavity having a dielectric constant greater than the dielectric constant of air, the dielectric material filling a sufficient amount of the cavity to require a reduction in size of the cavity to support a desired resonant mode. Preferably, the dielectric material exhibits at least one of a high reflectivity and a high thermal conductivity. Also preferably, the dielectric material exhibits a dielectric constant of at least 2. More preferably, the dielectric material exhibits a dielectric constant of at least 4. For example, the dielectric material may comprise boron nitride.
Preferably, the dielectric material occupies a substantial portion of the microwave cavity. For example, where lamp comprises a coupling slot for directing energy into the resonant cavity, the dielectric material occupies substantially the entire portion of the resonant cavity between the coupling slot and the bulb. If the bulb is spherical, the dielectric material may define a semi-spherical recess around the bulb. The dielectric material may support the bulb or, if the bulb is attached to a stem, the dielectric material may define an opening adapted to receive the stem.
The foregoing objects, features, and advantages of the invention are achieved individually and in combination. The invention should not be construed as requiring two or more of the features described herein unless expressly recited in the claims.